The present invention concerns a device for assessing the surface condition of a material and a method using said assessment device, especially for characterizing the softness to touch of a material.
It is important in several domains to determine the surface condition of a material or changes in the surface condition. The condition depends upon the material under consideration: fibrous material; textile; human or animal skin; human or animal hair or fur; paper for writing, printing, cleaning, hygiene, or packaging; metal, animal, mineral or vegetable material; wood; or plastic materials. For example, in textile manufacturing, fabric treatment might cause the appearance of microfibers, which increases fabric softness. In certain cases it is useful to quantify the modifications to the surface of a material in order to determine a measurement of softness to the touch. By way of example, this measurement of softness to touch may be used by manufacturers of laundry products, detergents, and household products to test the quality of their products just as it is done in the cosmetics industry.
At the present time a first type of apparatus for measuring the topography of the surface to be analyzed exists, for example, an apparatus using an optical, mechanical, or imaging method. The surface profile is then studied using several techniques:
Statistical methods: in this case, the profile is considered as a population of elements defined by two or three coordinates. Analysis concerns first, the height of the asperities (average, deviation from average, disparity-type, obliqueness, fineness, etc.) and then their distribution over the surface (average distance between two asperities, etc.)
The usual methods: used in signal processing, such as frequency analysis, temporal analysis, time-frequency analysis, etc.
Chaotic methods: such as fractal analysis.
A second type of apparatus exists which directly measures the behavior of a surface when it is rubbed using a mechanical palpator. In this case, the measured signal is studied in a transitory or permanent regime with the usual signal processing methods, the statistical or chaotic methods cited above.
Each of these different investigatory methods has its disadvantages. The statistical methods used to measure topography or rubbing actually lack the sensitivity required for certain applications because the information is gathered as a whole and important differences in the surface state may be buried in the signal, resulting in an analysis that lacks discrimination. Moreover, it is necessary to determine what is the most sensitive parameter of the surface for analysis, and it is rather difficult to extract a unique, universal parameter.
Insofar as the usual signal processing methods are concerned, they may be very precise in the case of periodic surfaces but they do not adapt well to non-periodic surfaces. Furthermore, they use comparative methods and never absolutes.
Finally, chaotic methods, particularly calculation of fractal dimensions, have the same disadvantages as statistical analysis because they consider all the data resulting from the measurement.
Numerous applications using these methods are known. However, these applications are not based upon actual analysis of an element vibrating in contact with the surface.
This is the specific case with the device described in publication number JP-A-10 269 868 for measuring the rugosity of an electrical cable displaced under a flexible plate. This device merely measures the deflection of the flexible plate.
This is also the case with the device described in publication number U.S. Pat. No. 5,672,929 for detection of vibrations generated by displacing a support such as a sheet of paper. The vibrations are then analyzed to determine contact and movement, but not the surface condition of the support.
The present invention proposes remedying these problems with an evaluation device and a method for analyzing a surface which may or may not have surface periodicity, characterizing it using one parameter, and comparing surfaces of completely different structures, textures, component materials, and possible surface treatments.
The present invention comprises a support to which at least one vibrating element is attached and is capable of vibrating upon contact with the surface of the material, with the vibrating element moving relative to the surface of the material. The evaluation device also comprises a means for measuring the particular vibration modes of the vibrating element in order to furnish a signal corresponding to said particular vibration modes, a device for processing and analyzing the signal in order to extract at least one element of data about the surface condition, as well as an interface to display the one or more elements of data.
In a particularly advantageous manner, the evaluation device may comprise a second processing device for transforming said data characterizing the surface condition into a value quantifying the material""s softness to touch as a function of at least one predefined criterion.
The material may be selected from the group comprising metals, organic, mineral, natural or artificial material, synthetic material, or a composition of several of these materials. In particular, it may be a living material, such as skin or hair.
The vibrating element may be selected from the group comprising metals, organic, mineral, natural or artificial material, synthetic material, or a composition of several of these materials.
The means for measuring the particular vibration modes of the vibrating element may consist of sensors which measure at least one physical dimension associated with the vibrating element, such as kinematic dimensions (displacement, speed, acceleration) or dynamic dimensions associated with the vibrating element (force, moment) or with the material (constraint, deformation, deformation speed). The sensors may also measure at least one dimension associated with the corresponding environment (acoustical and thermal dimensions). The sensor or sensors are founded on a technology selected from a group comprising at least the following technologies: mechanical, acoustical, electrical, electrostatical, electromagnetic, electronics, optical, optoelectronic, chemical, thermal, radioactive, or a combination of these technologies, using fluid as the media, the state of the fluid being chosen from the group comprising at least the viscous, liquid, or gaseous state.
Advantageously, the signal processing and analysis device produces signal analysis using a method selected from the group comprising at least mathematics or physics.
The analysis method is preferably a physics method designed to effect signal transformation selected from the group comprising at least Fourier transformation, time-frequency transformation, or wave transformation. Any other mathematics or physics method of analyzing an analog, discrete, quantified, or digital signal may also be used.
The vibrating element is attached to a support at an angle with a mechanical connection selected from the group comprising one of the following mechanical connections: unidirectional or bidirectional pivot, sliding pivot, spherical pivot with a finger, spherical pivot without a finger, linear, sliding, plane abutment, or point abutment, allowing it between 0 and 5 degrees of movement.
In a particularly advantageous method, the evaluation device of the invention comprises a protective housing for the vibrating element and its support, said housing comprising at least one opening for a portion of the vibrating element to pass through. The means for measuring the particular vibration modes, the processing and analysis device, and the interface may be partially or completely contained within the housing.
The invention also concerns a method using the evaluation device described above in which said evaluation device is move relative to the material so as to cause the vibrating element to vibrate, the particular modes of vibration by the vibrating element are measured using said means for measuring particular modes of vibration, and the resulting signal is processed and analyzed using the processing and analysis device in order to obtain at least the data corresponding to the surface condition of the material.
In a particularly advantageous embodiment, said data characterizing the surface condition of the material may be transformed into at least one value quantifying the softness to touch of the material according to at least one predefined criterion.